The difference between the pressure inside and outside of the bellows causes the bellows to expand or collapse, and this change in its dimensions causes a pointer to move over its dial showing the pilot the rate of climb or descent. Vertical-speed indicators are often called rate-of-climb indicators.
vertical stabilizer. See vertical fin.
vertical tape instrument. A tall rectangular instrument that displays the quantity of the parameter being measured by a movable strip of colored tape. The presentation resembles a vertical bar graph.
vertical vibration (helicopter operation). Up-and-down vibration of a helicopter caused by an out-of-track main rotor.
vertical visibility (meteorology). The distance one can see upward into a surface-based obscuration. It is also the maximum height from which a pilot in flight can recognize the ground through a surface-based obscuration.
vertigo. A type of spatial disorientation caused by the physical senses sending conflicting signals to the brain. Vertigo is specially hazardous when flying under conditions of poor visibility. The eyes send a signal to the brain telling it the airplane is in one condition, while the deep muscles, “the seat of the pants,” tell the brain the airplane is in another condition. The inner ear tells still another story, and the result is confusion
— vertigo.
Vertigo may cause pilot incapacitation, but may be minimized by confidence in the indication of the flight instruments.
very high frequency. See VHF.
very-high-frequency omnirange. See VOR.
very low frequency. See VLF.
Very signal. A type of emergency light signal used by ships and aircraft. A special pistol, a Very pistol, fires a cartridge that looks much like a shotgun cartridge. The cartridge sends up a ball of white or colored fire that can be seen for several miles during the day or night.
VFO (variable-frequency oscillator). An oscillator inside a communications radio receiver that produces radio-frequency alternating current. The frequency produced by the VFO can be changed until it is almost the same as the radio frequency of the carrier being received. When the output of the VFO is mixed with a continuous wave (CW) carrier, an audible signal is produced.
VFOs are used to make Morse code signals audible when they are transmitted by continuous wave (CW) transmission. When a VFO is used in this way, it is called a beat-frequency oscillator, a BFO.
VFR (visual flight rules). Flight rules adopted by the Federal Aviation Administration to govern aircraft flight when the pilot has visual reference to the ground at all times. VFR operations specify the amount of ceiling (the distance between the surface of the earth and the base of the clouds) and the visibility (the horizontal distance the pilot can see) that the pilot must have in order to operate according to these rules.
When the weather conditions are not such that the pilot can operate according to VFR, he or she must use another set of rules, instrument flight rules (IFR).
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